Zygomycetes – Biology Notes
General characteristics of Zygomycetes
- The group is named zygomycetes because of the formation of diploid resting spore called zygospore.
- They are mostly saprophytic and some are parasites on plants and animals.
- The plant body is mycelium which is well developed profusely branched and coenocytic.
- They reproduce asexually by endogenous non motile spores.
- Sexual reproduction takes place by conjugation and form a diploid structure zygospore.
- Zygospore give rise to the germ sporangium and germ spores which on germination give rise to new hyphae.
Sub division: Eumycotina
Mucor is a saprophytic fungus grows and decaying organic matter, rotten fruit, vegetables, animal dung etc. It is commonly known as pin mould. The plant body mycelium is long, branched, multinucleate, coenocytic filament. The individual thread of mycelium is known as hypha. Mucor consist of 3 types of hyphae. Prostrate hypha spreads over the substratum, subterranean hypha penetrate the substratum and aerial hypha (sporangiosphore) arises from the prostrate hypha.
Reproduction of Mucor Ascomycetes
Mucor Asexual Reproduction
It reproduces vegetatively by means of fragmentation. It reproduces asexually by means of aplanospores, chlamydospores, oidia etc. under favorable condition sporangiophore possess a sporangium on the top. A number of non-motile spores are formed by means of cleavage of multicellular protoplast of sporangium. At maturity sporangium brust and spores released out and germinate producing a germ tube and finally give rise to the profusely branched mycelium. The chlamydospores are formed in chains during unfavorable conditions by means of contraction of protoplast which on germination give rise to new mycelium. In some species (Mucor racemosus), growing in liquid media becomes septate and thin walled segments, oidia , which separate and multiply by budding, called torula condition.
Sexual reproduction in Mucor
Most of the species of Mucor are heterothallic and few are homothallic. In homothallic species conjugation takes place between the branches of the same mycelium whole in heterothallic species, fusion takes place between 2 different mating types i.e. +strains and –strains.
During sexual reproduction the hypha of opposite strains come close together and produce a club shaped protuberance called progametangia. They come in contact at their tips. Then septa is formed which separates the terminal gametangia and basal suspensor. Later the contact wall dissolves and 2 gametes fuse to form a diploid structure zygospore.
The zygospore after a period of rest, germinates, by producing germ tube (pro mycelium). It possesses a germ sporangium at its tip, in which meiotic division takes place and produces a number of haploid nuclei. Then the multicellular protoplast undergoes cleavage to produce non-motile germspores which on germination give rise to new hypha of Mucor.